Theoretically, the beta amylase enzyme becomes more denatured with higher temperatures, so the wort is [EDIT: "less"] fermentable. However, small temperature differences of a couple of degrees probably don't matter too much. It should become more noticeable at say 6 or 8 degrees difference, e.g., the difference between mashing at 148 F versus 156 F might be noticeable. Maybe.
More experiments are necessary to confirm real life results.
Another thing to keep in mind is that the malts we have today are way better modified and have way more enzymes than the same malts produced just ~15 years ago or more. High tech kind of stuff. Our maltsters are getting better and better everyday. So, what was very significant 50 years ago might not actually be significant at all anymore.